1. Field of the Invention
This invention relates to method and apparatus for pumping concrete to elevated heights and is especially useful for continuously lifting flowable concrete mix to forms used in the fabrication of annular structures such as concrete hyperbolic cooling towers.
In the construction of annular structures in the nature of hyperbolic cooling towers, upright base support pillars are first erected in position defining an inlet for air which is drawn upwardly through the final tower by natural convective draft. The concrete shell which rests on these supports is fabricated by erecting forms which are sequentially filled to present annular rings concentric with the center of the tower. After adequate curing of a respective ring, the forms are raised through an increment to define the next annular segment of the tower. By virtue of the changing diameter of the hyperbolic tower during its fabrication, the forms are of such nature that the circumferential extent thereof may be increased or decreased as necessary to comform to the hyperbolic design.
Since each of the annular concrete rings is allowed to set up and harden before the next annulus is formed, the shell itself may be used as a foundation for lifting the forms to the next higher elevation for fabrication of a succeeding ring. Generally speaking, appropriate scaffolding is provided in association with the forms so that workmen may implace reinforcing rod and control the introduction of concrete mix into the form cavity.
2. Description of the Prior Art
Heretofore, it has been conventional practice to station a tower crane at the center of the shell to be constructed with the rotatable jib at the top of the crane being rotatable through a 360.degree. arc. A winch line controlled from the cab of the tower crane may be lowered to the ground to pick up a concrete mix bucket which usually holds about two cubic yards of concrete. After the bucket is filled at the mix plant, it is raised by the winch line to the level of the circumferentially extending forms and the jib rotated through an arc at the same time that the bucket is moved to a lateral position overlying the forms so that the workmen may direct the concrete into the area of the forms next to be filled. This batch operation is continued until the entire perimeter of the forms have been filled with concrete mix. The bucket is then either run out toward the end of the jib or brought back toward the tower mast and lowered to the mix plant accompanied by the necessary rotation of the jib so that a fresh batch of the mix may be loaded into the bucket. Each time the bucket is lifted, it is swung to a position for deposit of material in the next adjacent area of the cavity to be filled.
A typical concrete hyperbolic cooling tower is, for example, about 450 feet high, has a diameter of 330 feet at ground level, 300 feet at the commencement of the concrete shell, 163 feet wide at the throat and 180 feet in diameter at the top. Generally as much as 600 cubic yards of concrete must be hoisted to the form level during each 8 hour working day for the thicker parts of the shell, and at least 150-160 cubic yards per day during fabrication of the throat part of the tower. Generally speaking, the forms are lifted about 6 feet per day with each pour being allowed to cure to a required degree, and then the forms shifted upwardly to their next incremental position. The circumference of these climbing forms is adjusted as necessary to define the required hyperbolic shape. Since circumferential as well as upright reinforcing bars are provided in the form cavity, as well as the transverse bars which serve as supports for the forms, one of the challenges that must be overcome in use of the tower crane-batch bucket elevation of concrete to the construction site is the maneuvering of that bucket around the re-bars while at the same time swinging the bucket as necessary to effect even deposit of the mix between the forms. One other inherent disadvantage of the bucket method of raising concrete to the construction level is the time consumed in lowering the bucket back down to ground level and then returning the same to the location where the next area is to be filled. Even the use of more than one bucket so that one can be filled while another is being unloaded does not save a great deal of time, by virtue of the fact that much time is lost in attempting to properly position and maneuver the bucket as concrete is discharged through the bottom gate thereof.